There has been known a method of manufacturing a semiconductor device where a glass layer for passivation is formed such that the glass layer covers a pn junction exposure portion in a process of manufacturing a mesa semiconductor device (see patent document 1, for example).
FIG. 8(a) to FIG. 8(d) and FIG. 9(a) to FIG. 9(d) are views for explaining such a conventional method of manufacturing a semiconductor device. That is, FIG. 8(a) to FIG. 8(d) and FIG. 9(a) to FIG. 9(d) are views showing respective steps of the conventional method.
The conventional method of manufacturing a semiconductor device includes, as shown in FIG. 8(a) to FIG. 8(d) and FIG. 9(a) to FIG. 9(d), “semiconductor substrate forming step”, “trench forming step”, “glass layer forming step”, “photoresist forming step”, “oxide film removing step”, “roughened surface region forming step”, “electrode forming step”, and “semiconductor substrate cutting step” in this order. Hereinafter, the conventional method of manufacturing a semiconductor device is explained in order of steps.
(a) Semiconductor Substrate Forming Step
Firstly, a p+ type diffusion layer 912 is formed by diffusion of a p type impurity from one surface of an n− type semiconductor substrate (n type silicon substrate) 910, and an n+ type diffusion layer 914 is formed by diffusion of an n type impurity from the other surface of the n− type semiconductor substrate 910 thus forming a semiconductor substrate in which a pn junction arranged parallel to a main surface of the semiconductor substrate is formed. Thereafter, oxide films 916, 918 are formed by thermal oxidation on a surface of the p+ type diffusion layer 912 and a surface of the n+ type diffusion layer 914 respectively (see FIG. 8(a)).
(b) Trench Forming Step
Next, a predetermined opening portion is formed on the oxide film 916 at a predetermined position by photo etching. After etching the oxide film, subsequently, the semiconductor substrate is etched thus forming a trench 920 having a depth which goes beyond the pn junction as measured from one surface of the semiconductor substrate (see FIG. 8(b)).
(c) Glass Layer Forming Step
Next, a layer made of glass composition for protecting a semiconductor junction is formed on an inner surface of the trench 920 and a surface of the semiconductor substrate in the vicinity of the trench 920 by electrophoresis, and the layer made of glass composition for protecting a semiconductor junction is baked so that a glass layer 924 for passivation is formed on a surface of the trench 920 (see FIG. 8(c)).
(d) Photoresist Forming Step
Next, a photoresist 926 is formed such that the photoresist 926 covers a surface of the glass layer 912 (see FIG. 8(d)).
(e) Oxide Film Removing Step
Next, the oxide film 916 is etched using the photoresist 926 as a mask so that the oxide film 916 at a portion 930 where a Ni-plating electrode film is to be formed is removed (see FIG. 9(a)).
(f) Roughened Surface Region Forming Step
Next, a surface of the semiconductor substrate at the position 930 where the Ni-plating electrode film is to be formed is subjected to surface roughening treatment thus forming a roughened surface region 932 for enhancing adhesiveness between a Ni plating electrode and the semiconductor substrate (see FIG. 9(b)).
(g) Electrode Forming Step
Next, Ni plating is applied to the semiconductor substrate thus forming an anode electrode 934 on the roughened surface region 932 and forming a cathode electrode 936 on the other surface of the semiconductor substrate (see FIG. 9(c)).
(h) Semiconductor Substrate Cutting Step
Next, the semiconductor substrate is cut by dicing or the like at a center portion of the glass layer 924 thus dividing the semiconductor substrate into chips which constitute mesa semiconductor devices (pn diodes) respectively (see FIG. 9(d)).
As has been explained heretofore, the conventional method of manufacturing a semiconductor device includes the step of forming the trench 920 which goes beyond the pn junction as measured from one surface of the semiconductor substrate where the pn junction arranged parallel to the main surface is formed (see FIG. 8(a) and FIG. 8(b)), and the step of forming the glass layer 924 for passivation in the inside of the trench 920 such that the glass layer 924 covers the pn junction exposure portion (see FIG. 8(c)). Accordingly, in the conventional method of manufacturing a semiconductor device, by cutting the semiconductor substrate after forming the glass layer 924 for passivation in the inside of the trench 920, mesa semiconductor devices having a high breakdown voltage can be manufactured.